A brake is typically a mechanical device designed to inhibit motion. Brakes commonly use friction to convert kinetic energy into heat, though other methods of energy conversion may be employed. For example regenerative braking converts much of the energy to electric energy, which may be stored for later use.
On vehicles, braking systems are employed to apply a retarding force, typically via frictional elements at the vehicle's rotating axles or wheels, to inhibit vehicle motion. Friction brakes often include stationary shoes or pads that are lined with friction material and configured to be engaged with a rotating wear surface, such as a rotor or a drum. Common configurations include shoes that contact to rub on the outside of a rotating drum, commonly called a “band brake”, a rotating drum with shoes that expand to rub the inside of a drum, commonly called a “drum brake”, and pads that pinch a rotating disc, commonly called a “disc brake”.
Modern vehicles typically use a hydraulic force to press the aforementioned shoes or pads against the respective rotating disc or drum, which slows the disc or drum and its attendant wheel. Generally, vehicle friction brakes store thermal energy in the disc brake or drum brake while the brakes are being applied and then gradually conduct the stored heat to the ambient. Additionally, during the process of retarding a vehicle, the friction surfaces of shoes or pads, as well as of the respective drums and rotors, experience wear. Accordingly, such friction surfaces must be periodically renewed or replaced.